Relentless Forward Progress_ A Guide to Running Ultramarathons - Bryon Powell [75]
While improvement in resting oxygen saturation plateaus at around eight days, oxygen saturation during exercise continues to increase through three weeks of altitude acclimation. A multitude of adaptations make this possible despite ventilation having plateaued long ago.
In the first two or three days after arriving at altitude, your basal metabolic rate increases before returning to normal between one and three weeks after arrival. The basal metabolic rate is the body’s energy expenditure and it makes up a majority of a non-exercising person’s daily caloric needs. Because we can only sustain burning limited number of calories per hour during an ultramarathon, diverting some of these calories due to a small but significant increase in basal metabolic rate may decrease athletic performance.
For most people, an increase in red blood cell count is likely the first adaptation they think of when contemplating altitude acclimation. However, increased red blood cell count, which increases the ability to transport oxygen, is one of the body’s slowest adaptations to altitude. For example, a lowlander traveling to 10,000 feet in Leadville, Colorado, would not experience an increase a change in red bloods within his or her first 10 days in town.
Arriving and Acclimating at Altitude
Ideally, you would arrive at altitude three or more weeks before competing in an event at or above 8,000 feet. However, to be realistic, you’re likely to spend a week or less at race altitude prior to competing. With that in mind, it’s important to determine when you should ideally arrive within the week prior to race day.
During the first week at altitude, minimizing the short-term ill effects of altitude is as important as performance-related acclimation, if not more so. In particular, acute mountain sickness (AMS) is common among lowlanders arriving at moderate elevation (as low as 6,500 feet) and more acclimated individuals ascending thousands of feet above the altitude to which they’re acclimated. Given the altitudes of ultras in the North America and Europe, the vast majority of AMS cases will be unpleasant, but nothing more. Symptoms can include headache, difficulty sleeping, drowsiness, dizziness and lightheadedness, fatigue, loss off appetite, nausea or vomiting, rapid heart rate, and shortness of breath during exertion. Or, as one book has put it, AMS resembles a case of “flu, carbon monoxide poisoning, or a hangover.”* These symptoms can occur at any time after arriving at altitude, not just while running. The symptoms of AMS can present themselves within a few hours of ascent, but often on the second or third day at altitude. Symptoms typically subside within a day or two of onset. If you or someone you’re with develops an extremely severe headache or vomiting that’s not directly attributable to an aspect of ultrarunning, carefully monitor for other symptoms of high-altitude cerebral edema described below.
* The Mountaineers. Mountaineering: The Freedom of the Hills, seventh edition. Seattle: Mountaineers Books, 2003.
Be aware that a previous lack of AMS at a given altitude does not mean it won’t occur the next time you’re at that altitude. I’ve generally fared well in ascending to high altitude, but in the summer of 2009 I traveled to 10,000 feet in Leadville while acclimated to 6,000 to 7,000 feet and was still greeted by the worst headache of my life the day after my arrival.
With the effects of AMS in mind, those who can’t manage an acclimation period of more than a week are best off arriving four or more days before the event. If that’s not possible, arrive at altitude as close as possible to the start of the event to limit the onset of AMS and short-term performance decreases due to the initiation of acclimation.
Whenever you arrive at altitude, you are likely to experience a decrease in thirst and appetite. Therefore, upon arrival and in the days